1. Field of the invention
The invention relates to an exhaust manifold.
The exhaust manifold may form part of an exhaust system for an internal combustion engine of a motor vehicle. The internal combustion engine consists, for example, of a gasoline engine and has, for example, a plurality of cylindrical combustion chambers in which a piston which can be moved back and forth is arranged. However, the engine might instead be in the form of a rotary piston engine and have combustion chambers containing a rotary piston. Each combustion chamber is connected to an exhaust outlet of the internal combustion engine.
2. Description of the prior art
An exhaust manifold disclosed in German Utility Model 295 05 660 has a plurality of individual pipes which are formed from straight pipe sections and whose inlets can be connected to the exhaust outlets of the internal combustion engine and whose ends facing away from the inlets enter a horizontal collecting pipe at right angles to their axes. Each pipe section contains catalyst means not described in detail. The cross-sectional areas of the catalyst means present in the pipe sections or individual pipes are evidently at most about the same size as the cross-sectional areas of the inlet orifices of the pipe sections. The catalyst means therefore give rise to a large resistance to flow and a large pressure drop or opposite pressure which reduces the effective power of the engine. Moreover, the collecting pipe also contains catalyst means which further increase the resistance to flow and the opposite pressure. Since the exhaust outlets of the engines generally have approximately horizontal axes and are often arranged fairly high up on the engine and relatively high above the vehicle bottom, for space reasons it is often inexpedient to connect the exhaust outlets of the engine to a horizontal collecting pipe by straight pipe sections.
FIGS. 7 to 10 of French Publication 2 179 689 show exhaust manifolds having a plurality of pipes which are connected to exhaust outlets of an internal combustion engine and contain catalyst means. However, the catalyst means of this exhaust manifold also have only small cross-sectional areas transverse to the direction of flow of the exhaust gases flowing through them or require a plurality of sharp deflections of the exhaust gas and the passage of the exhaust gas through cavities having small cross-sectional areas. The catalyst means and/or the gas passage from and to the catalyst means therefore give rise to high resistances to flow and opposite pressures in these known exhaust manifolds too and, particularly in the case of the variants according to FIGS. 9 and 10, inhomogeneous flow distributions in the catalyst means.
German Publication 42 36 893 discloses an exhaust pipe connected to an exhaust outlet of an internal combustion engine. A curved section of this contains catalyst means having a stack of plates. These catalyst means have the disadvantages that their cross-sectional areas are at most approximately the same as those of the passage of the remaining pipe and that their exhaust gas passages are of different lengths depending on the radius of curvature, so that the exhaust gas is purified to different extents in the various passages. Furthermore, the production of such catalyst means is difficult and expensive.
U.S. Pat. Ser. 5 330 728 discloses catalytic converters whose housing has an inlet, a catalytic converter section containing catalyst means and an outlet. The inlet and the outlet are offset relative to one another and have axes parallel to one another, while the axis of the catalytic converter section and the passages of the catalyst means are inclined relative to these axes. The exhaust gas entry surface and the exhaust gas exit surface of the catalyst means are flat and parallel to the axes of the inlet and outlet. These catalytic converters are apparently intended to be arranged below the vehicle bottom and not to be arranged in the individual pipes of an exhaust manifold. For space reasons, it would also not be expedient to install such catalytic converters in an exhaust manifold. Furthermore, the exhaust gas is greatly deflected immediately after the catalyst means, the housing having, on one side of the exhaust gas exit surface of the catalyst means, a wall which is directly adjacent to said surface and which makes a fairly acute angle with the exhaust gas exit surface. During operation, a pressure gradient therefore forms over the exhaust gas exit surface and influences the exhaust gas flow in the catalyst means and makes it inhomogeneous. This impairs the efficiency of the catalyst means.